Cigarette smoking remains the number one cause of premature morbidity and mortality in the United States. National data show reductions in smoking prevalence among all age groups except for 18 to 24 year old young adults. Smoking prevalence in this age group is estimated at 24%, and this rate has held steady since 2003. National data indicate that compared to older adults, young adults are less successful at quitting, and they use treatment less often. Even though a sizeable proportion (72%) of young adult smokers are motivated to quit, and 49% have made a serious attempt to quit in the past year, only 4% of young adult smokers who attempted to quit in 2005 reported using behavioral treatment. Randomized trials of cessation treatments that report outcomes by age group show comparable outcomes for young adult and other adult smokers. Thus, quit rates among young adult smokers could improve with increased reach of evidence-based cessation treatments into this population. The underlying premise of the proposed study is that the development of effective strategies aimed to increase demand for evidence-based smoking cessation treatments among young adult smokers will accelerate rates of cessation in this key target population. The proposed study applies innovative research methods to achieve the following specific aims: (1) Implement a multi-phase market test strategy to develop a series of theory-driven internet- based messages to encourage use of behavioral cessation treatments among young adult smokers; (2) Implement a randomized controlled efficacy study to identify a minimum of 4 highly efficacious communications; (3) Implement an interrupted time series (ITS) study to assess the effectiveness and cost effectiveness of the communications under real-world conditions to increase young adult smokers' participation in evidence-based behavioral interventions. The ITS will provide precise detection of the magnitude and duration of trends in the effectiveness of the messages over time in stimulating demand for cessation treatment among young adult smokers; and (4) Conduct a longitudinal cohort study with a sample of young adult treatment participants in order to: (a) Describe patterns and degree of engagement with treatment, and (b) Model factors associated with use of treatment, smoking cessation attempts, and successful smoking cessation.